This application claims priority from Korean Patent Application No. 10-2004-0008173, filed on Feb. 7, 2004 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to an optical pickup, and more particularly, to an optical bench, on which metal wirings and optical parts can be formed, disposed on a substrate on which a photo detector and a silicon optical bench (SiOB) are monolithically formed, a thin optical pickup that employs the optical bench, and a method of manufacturing the optical bench.
2. Description of the Related Art
Recently, the use of mobile information devices such as PDAs, mobile phones, digital cameras, and camcorders has rapidly increased. To record and read data to and from such information devices, optical pickup devices are essential, and techniques of producing optical pickups for mobile information devices that have become further miniaturized are being developed.
FIGS. 1A and 1B are respectively a perspective view and a cross-sectional view illustrating an optical bench used for a conventional thin optical pickup.
The conventional optical bench includes a silicon substrate 12, a light source stand 20, a metal wiring 14 formed on the silicon substrate 12 and the light source stand 20, bonding pads 22, and solder pads 16.
In a conventional silicon optical bench, a light source such as a laser diode is mounted on the light source stand 20, and light emitted from the light source is incident on a 45° tilted mirror surface 24, which is a crystal surface of the silicon substrate 12 etched to have a {111} orientation. That is, a light beam emitted from the light source is spread out with a certain angle and then is incident on an Si{111} mirror surface with a predetermined spot size. Accordingly, if the light source stand 20 does not have a predetermined height with respect to a bottom surface 30 of the substrate 12 between the light source stand 20 and the mirror surface, some of the light emitted from the light source can not reach the mirror and is lost when it hits the bottom surface 30 of the substrate 12.
Therefore, in order for all the light emitted from the light source within a predetermined angle to reflect from the mirror surface 24 without loss, the light source stand 20 must have a certain height with respect to the bottom surface 30 of the silicon substrate 12. An electrode for supplying power to the laser diode is formed on the light source stand 20, and the light source of the laser diode is a flip-chip bonded by a solder bumper 16 composed of Au/Sn on the electrode.
In order to form a step difference between the bottom surface 30 of the silicon substrate 12 and the light source stand 20, the light source stand 20 is formed by dry etching (for example, reactive ion etching) the silicon substrate 12, and then, the mirror surface 24 having a 45° tilted Si{111} crystal surface 24 and the bottom surface 30 are formed by wet etching. The reason that light source stand 20 is formed by dry etching is to prevent the formation of a hollowed groove parallel to a surface of the silicon substrate 12. However, conventionally, due to the sequence of processes, such a deep trench is inevitably formed in the vicinity of the light source stand 20.
FIG. 2A is a cross-sectional view illustrating a problem that occurs when a metal wiring is formed on an optical bench used for a conventional thin film optical pickup by wet etching.
Referring to FIG. 2A, after forming a metal layer on a silicon substrate 12 to form a metal wiring 14, when coating a photoresist for patterning the metal layer to the metal wiring 14 using spin coating or spray coating, the portion of the photoresists at the corner portions A and B are peeled off.
After patterning the photoresist using a lithography process, the metal layer must be wet etched using the patterned photoresist as a mask. At this time, the portion of the metal layer an the corner portions A and B are removed. Therefore, the metal wiring is not connected at the corner portions A and B. Also, in the deep trench formed in the vicinity of the light source stand 20, the photoresist may remain after developing due to insufficient exposure.
FIG. 2B is a cross-sectional view illustrating a problem that occurs when performing a lift-off process for forming a metal wiring on an optical bench used for a conventional thin film optical pickup.
FIG. 2B illustrates a problem that occurs when performing a lift-off process to avoid the wet etching problem depicted in FIG. 2A. After coating a photoresist on an insulating film 18 on the silicon substrate 12, the photoresist is patterned to a shape opposite to the metal wiring 14, and then, a metal layer is deposited on the patterned photoresist. At this time, the photoresist is generally coated thickly on the bottom surface of the deep trench, and developing can not be sufficiently performed since an insufficient amount of light reaches the bottom of the deep trench or the process may take a long time. If the developing is performed excessively to remove the photoresist in the trench, too much of the photoresist on the surface of the silicon substrate 12 is removed resulting in an increased width of the metal wiring which can cause difficulty for maintaining a gap between wirings. If the developing is not sufficient, since the photoresist remaining in the trench C can not be removed completely, the metal wiring 14 is removed when removing the photoresist in a subsequent lift-off process, thereby disconnecting the metal wiring 14.